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Policies requiring people to stay home during the COVID-19 pandemic have resulted in dramatic reductions in global carbon dioxide emissions. At their lowest point, CO2 emissions dropped by 17% in early April, as China was ramping its economy back up and the US and other countries slowed theirs. Researchers expect that these extreme decreases won’t last the entire year and estimate that daily CO2 emissions will be down by at least 4% overall for 2020 (Nat. Clim. Change 2020, DOI: 10.1038/s41558-020-0797-x).

The 17% decline is the biggest change in CO2 emissions since World War II, and may turn out to be the most precipitous drop ever observed, says Robert Jackson, an earth system scientist at Stanford University.

Record drop

Because of stay-at-home orders, CO2 emissions have fallen dramatically during the COVID-19 pandemic.Source:Nat. Clim. ChangeNote: MtCO2 is million metric tons of carbon dioxide.

To estimate changes in CO2 emissions, Jackson and a team of researchers led by University of East Anglia climate scientist Corinne Le Quéré used data on traffic, flights, steel production, electricity usage, and more. The main contributor to the decline in CO2 emissions was a decrease in passenger vehicle traffic. CO2emissions cannot currently be measured directly on a global scale. So the team relied on traffic information and mobile phone data to estimate emissions and monitor changes in near real time.

Each country’s peak decline was about 25%; in the US the changes were even more extreme, with daily CO2 emissions falling by 32% from April 7 to 20. “Who could have imagined that US emissions would drop by one-third for a couple weeks in April?” Jackson says. “Absolutely unprecedented.”